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Chapter 5
Deformation of the Crust
Section 5.2
What are the results of stress on
the surface of the earth?
Strain
strain any change in a rock’s shape or volume
caused by stress
• When stress is applied slowly, the deformed
rock may regain its original shape when the
stress is removed.
• The amount of stress that rock can withstand
without permanently changing shape is limited.
• If a stress exceeds the rock’s limit, the rock’s
shape permanently changes.
Folding
fold a form of strain in which rock layers
bend, usually as a result of compression.
• Although a fold commonly results from
compression, it can also form as a result
of shear stress.
Questions
• What is a strain?
– any change in a rock’s shape or volume
caused by stress
• What is a fold?
– a form of strain in which rock layers bend,
usually as a result of compression.
Types of folds
• An anticline is a fold in which the oldest
layer is in the center of the fold. Anticlines
are commonly arch shaped.
• (Sad face)
Question
• What is an anticline?
– fold in which the oldest layer is in the center of
the fold
• Draw the shape of an anticline.
Types of folds
• A syncline is a fold in which the youngest
layer is in the center of the fold. Synclines
are commonly bowl shaped.
• Smiley face
Question
• What is a syncline?
– fold in which the youngest layer is in the
center of the fold
• Draw an syncline.
Types of folds
• A monocline is a fold in which both limbs
are horizontal or almost horizontal.
Monoclines form when one part of Earth’s
crust moves up or down relative to another
part.
• steps
Question
• What is a monocline?
– fold in which both limbs are horizontal or
almost horizontal
• Draw a monocline.
Faulting
fault a break in a body of rock along which one
block slides relative to another
• Stress on rock can cause rock to break.
• Breaks in rock along which there is no
movement of the surrounding rock is called a
fracture.
• A break along which the surrounding rock
moves is called a fault.
See page 86 in your textbook for faults
Normal Faults
• A normal fault is a fault in which the
hanging wall moves downward relative to
the footwall.
• Form at divergent boundaries.
• Normal faults may occur as a series of
parallel fault lines, forming steep, steplike
landforms.
Reverse Faults
• When compression causes the hanging wall to
move upward relative to the footwall, a reverse
fault forms.
• A thrust fault is a special type of reverse fault in
which the fault plane is at a low angle or is
nearly horizontal.
• Reverse faults and thrust faults are common in
steep mountain ranges, such as the Rockies and
the Alps.
Strike-Slip Faults
• In a strike-slip fault, the rock on either
side of the fault plane slides horizontally in
response to shear stress.
• Strike-slip faults commonly occur at
transform boundaries.
• The San Andreas Fault is an example of a
strike-slip fault.
Question
• What are the four types of faults?
– Normal Faults
– Reverse Faults
– Strike-Slip Faults
– Thrust Faults